The overall objective of this study is to develop and to use the mouse mammary tumor system as an experimental model where immunotherapeutic procedures may be evaluated. Treatment procedures will be compared with respect to their ability to induce, enlarge, and maintain host resistance to tumor growth, and to assay the effects of treatment on the host's immune resistance factors. The planned research aims to develop the mouse mammary tumor system for exploring and testing procedures of immunotherapy. The experiments are designed to reveal fundamental aspects of tumor immunogenicity and of anti-tumor immunity, and to indicate effective ahd hazardous immunotherapeutic procedures. The objectives are mainly four: (1) To study mammary tumorigenesis and to study the antigenic strength, frequency of occurrence and interrelationships of virus-associated tumor antigens and tumor-specific antigens in Mammary Tumor Virus (MTV) plus Nodule Inducing Virus (NIV)-infected C3H mice. (2) To study mammary tumorigenesis and tumor antigenicity in MTV-free, NIV-infected C3Hf mice. (3) To study the effects on host resistance of immunotherapy using killed tumor cell preparations at progressive stages of neoplastic growth, and at progressive stages of recovery after surgical cure. (4) To study tumor characteristics related to metastasis and to study host resistance factors that can influence the establishment and growth of disseminated tumor cells.